A lithographic photomask, or reticle, conventionally has a protective pellicle (thin organic membrane on a metal frame) that is glued to the front surface, or active side, of the reticle. In the following, the term pellicle is used for the combined membrane and frame. This pellicle often must be removed during the reticle lifetime, especially for a reticle exposed at 193 nm, which develops crystal growth (so-called haze) on the front surface under the pellicle during use. The haze must be removed regularly, typically at intervals of a few months, by cleaning the reticle (which requires removal of the pellicle). Aggressive cleaning processes, such as sulfuric acid and megasonic cleaning must be used to remove traces of the pellicle adhesive. Not only can these techniques lead to damage or additional contamination of the reticle, thereby requiring further repair, cleaning, and inspection, which are costly and time-consuming, but also sulfuric acid leaves sulfate residues, a known source for haze. Further, the reticle may be damaged beyond repair and require replacement. Moreover, the pellicle cannot be reused after being removed and, therefore, must be replaced. Consequently, the entire process must be performed in a mask shop, rather than in the semiconductor fabrication plant (fab), which further adds to the cycle time. Another consequence of the pellicle being glued to the reticle (and therefore not being easily removable) is that in the current standard reticle production flow, to avoid superfluous pellicle removal, a particle (“starlight”) inspection prior to mounting the pellicle is required, in addition to the final post-pell inspection after pellicle mounting.
A need thus exists for methodology enabling a pellicle to be removably affixed to the reticle, without the use of an adhesive.